This invention relates to a new method and apparatus for detecting the vibration of the propeller blades in mechanical aerators which have become obstructed by debris, and further relates to a means for removing the obstructing debris from the aerator blades.
Mechanical aerators are commonly used by textile and chemical companies, pulp and paper mills, food processors and municipalities to increase the oxygen content in standing bodies of liquid. Where impurities are present in liquid, an increased oxygen level supports microbes, which remove and process the impurities. For example, microbial breakdown of bacteria is an essential step in sewage treatment. Mechanical aerators are typically positioned at intervals in a pond of liquid, and, therefore, it is not easy for operations personnel to visually monitor the aerators.
Commonly, mechanical aerators include a float or platform to support the aerator in the liquid, a propeller to draw the liquid through the aerator, and a motor and shaft to turn the propeller. From a bottom passage, liquid enters the aerator and is lifted by the propeller through a top passage and out of the aerator. The formation of the top passage directs the liquid exiting the aerator upward and away form the device so that liquid droplets exiting the aerator descend between 2 and 6 feet before reaching the surface of the liquid. As the exiting droplets descend, they are exposed to the atmospheric gases, which are 21% oxygen.
A problem occurs when rags or other debris are drawn into the aerator and become attached to the propeller. Typically the propeller, turning at 1760 to 1800 rpm, is located 2 to 4 feet below the motor and has no end stabilization to prevent its horizontal movement. Debris can attach to the propeller causing an imbalance in the propeller. The imbalance in the propeller causes vibrations which are transmitted up the motor shaft and into the motor, ultimately causing the motor to fail. This problem is common, and, as a result, the life of a mechanical aerator motor in some cases is less than 1 year.
Because mechanical aerators are located in a pond of liquid, and, therefore, not subject to convenient visual monitoring by operations personnel, it is desirable to have a means of automatically detecting and dislodging debris which becomes caught on the aerator propeller. In order to prevent mechanical aerator motors from failing as described above, the method and apparatus of the present invention provides a means for detecting the excessive vibration of the propeller blades in mechanical aerators which occurs when the blades have become obstructed by debris, such as rags or other materials. The present invention includes a waterproof vibration sensor mounted within sensing range of the rotating shaft of the aerator propeller. The sensor is operably connected to the propeller motor so that when the sensor detects excessive motor shaft vibrations caused by debris attached to the propeller, the motor is automatically shut down and then run in the reverse direction causing the debris to be thrown off the propeller. Once the debris have been dislocated from the propeller, the motor is restarted in the forward direction. If the sensor continues to detect excessive motor shaft vibration, the motor will once again be shut down and then run in the reverse direction. If after a predetermined number of reversals and restarts in the forward direction, the debris have not been removed from the propeller, an alarm will be activated signaling the operations personnel that the aerator requires operator attention.
If the automatic propeller reversal and restart in the forward direction fails to dislocate the debris, the system can be manually run in the forward or reverse direction as desired by the operator. Consequently, the present invention also provides a means for manually controlling shut down, reversal, and restart of the propeller motor to remove debris.
The present invention also includes an alarm means for indicating when the aerator motor has failed due to motor breakdown, such as bearing deterioration and wire breakage.